1. Field of the Invention
The invention concerns a liquid crystal display.
2. Description of the Prior Art
According to P. Maltese and C. M. Ottavi (Alta Frequenza, Vol. 47, No. 9, 1978) a nematic field effect liquid crystal display with negative anisotropy of the dielectric constants and homeotropic orientation to the boundary is known that has a right or left circular polar polarizer in front of and a left one behind the liquid crystal cell.
From the French patent document No. 2 201 005 of the same inventors a liquid crystal display with negative dielectric anisotropy and homeotropic orientation of the liquid crystal is known. The liquid crystal is located between two carrier plates, of which at least one is transparent. The thickness of the liquid crystal layer is chosen as close as possible to its optimum specific thickness. This thickness is normally not larger than 5 .mu.m. The display is activated in transmission. The display can, however, also be used in reflection operation. For this purpose electrode 8 is at the same time a metallic mirror. It is not mentioned from what material this mirror should be made. In this arrangement only a polarizer is needed. In order to achieve an orientation of the liquid crystal the contact surfaces of the liquid crystal cell are first cleaned with a mixture of sulfuric acid and chromic acid and then rinsed with distilled water. Subsequently these surfaces are rubbed with a chamois and scouring powder in a specific direction.
For this effect very narrow (3-10 .mu.m) cell intervals as parallel in plane as possible are needed. Since up to now this requirement for a small variation in the thickness of the intervals could only be achieved through thick glass plates, operation with an external reflector involved a strong parallax. An internal reflector, as is known from the literature above, has the disadvantage that the display element is visible even when the power is not turned on. If the same liquid crystal layer is used as in transmission operation, i.e. MBBA, IEBBA mixture, the layer is about 2 .mu.m thick. Such thin layers cannot be achieved at present.